The best way to ensure a healthy lawn in Colorado is to use a variety of grass that is suitable to the local climate. Perennial rye grasses do very well as do other native grasses. However, if you are looking for a traditional deep green, lush lawn, grasses like Kentucky Bluegrass can grow well with proper care and maintenance.
Colorado is a semi-arid state. Although many years, the state gets enough water for some varieties of grass, especially local xeriscaping grasses, traditional green lawns almost always need some additional irrigation. Without irrigation, most lawns will turn brown by mid-summer. In some drier years, the lack of water may actually kill some kinds of grasses. To avoid wasting water, don't give your lawn more than 1/4 inch of water per hour. Give your traditional grass lawns about an inch of water per week by watering in the morning and evening. Try to avoid watering your lawn during the heat of the day. Watering during the heat of the day results in water evaporating instead of soaking in to the soil.
Colorado has a number of common lawn weeds. From crabgrass and foxtail to barnyard grass and goosegrass, if your lawn is thin it can become susceptible to these types of weeds. In some cases, simply mowing the weeds or invasive grass to prevent seeding can prevent them from being a problem in subsequent years. Make sure your lawn has enough water and is thick. Thick lawns make it harder for weeds to take root. Although you can use commonly available herbicides on weeds, if your infestation isn't severe, digging them up may be a good solution.
Necrotic Ring Spots
Necrotic ring spots is a perennial disease that primarily affects Kentucky Bluegrass in Colorado. Necrotic ring spots are caused by a fungus and often appear in late summer. Necrotic ring spots tend to begin 2 to 3 years after the lawn has established. The ring spots can look like large rings or simply dead patches of grass in Kentucky Bluegrass based lawns. Poor soil drainage often contributes to necrotic ring spots. To avoid this disease, avoid over watering and and try not to remove more than 1/3 of the grass blades in a single mowing. In some cases, the necrotic ring spots will disappear by the following spring. In other cases, you may need to seed the areas with a variety of grass resistant to the fungus, such as a local perennial rye grass. If the difference in color and texture is unacceptable, you might find success with one of several commercial lawn fungicides.